In general, an electrically conductive organic polymer called polyaniline is a polymer having a quinonediimine structural unit represented by the following formula as the main repeating unit ##STR2## and which contains a dopant (U.S. Pat. No. 4,615,829). In more detail, the electrically conductive organic polymer is a quinonediimine.phenylenediamine type polyaniline having a quinonediimine structural unit and a phenylenediamine structural unit represented by the following formula as the main repeating units ##STR3## and which is doped with a protonic acid.
It is generally said that protonation of nitrogen atom in the quinonediimine structural unit in such a polyaniline is indispensable to exhibit the electrical conductivity.
In the above formula, m and n show molar fractions of the quinonediimine structural unit and the phenylenediamine structural unit," respectively, in the repeating unit, provided that 0&lt;m&lt;1, 0&lt;n &lt;1, and m+n=1.
A film comprising the electrically conductive polyaniline can be obtained by dissolving a solvent-soluble quinonediimine-phenylenediamine type polyaniline in a proper solvent, casting the solution followed by drying to form a film, and subjecting the film to a doping treatment (protonic acid doping) by immersing the film in an aqueous solution of a protonic acid as described in, e.g., JP-A-3-28229 (corresponding to U.S. patent application Ser. No. 07/413,502) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Further, JP-A-3-52929 describes that an electrically conductive polyaniline film is obtained by dissolving an imino-p-phenylene type polyaniline having an imino-p-phenylene structural unit shown by the formula ##STR4## as the main repeating unit in a solvent, adding thereto a proper oxidizing agent, and casting the mixture to form the film. According to this process, the imino-p-phenylene type polyaniline is oxidized and converted into a quinonediimine-phenylenediamine type polyaniline. In this case, the polyaniline is also doped with the anion of the oxidizing agent. Since doping in this case is accompanied by an oxidation reaction, the doping is usually called oxidation doping.
As described above, in order that a polyaniline has an electrical conductivity, it is necessary that the polyaniline has both the quinonediimine structure and the phenylenediamine structure in the molecule and also it is necessary that the nitrogen in the quinonediimine structure is protonated (doped). However, hitherto, for doping with the protonic acid as above, a long time is usually required. The doping time differs according to the kind of the protonic acid used and the properties of the polyaniline film, such as the film thickness, porosity, etc., and in the polyaniline film having a thickness of about 20 .mu.m, for imparting an electrical conductivity of at least 1 S/cm, it is required to immerse the film in an aqueous hydrochloric acid solution for several hours. When p-toluenesulfonic acid is used as the acid, several days are sometimes required. Requirement of such a long time for doping is disadvantageous for the industrial production of an electrically conductive polyaniline film.
On the other hand, it is described in JP-A-60-133027 and Faraday Discuss. Chem Soc., 88, 317(1989) that a quinonediimine-phenylenediamine type polyaniline can be obtained by subjecting the powder of an imino-p-phenylene type polyaniline to an oxidation doping treatment with an acetonitrile solution of ferric chloride or with hydrogen peroxide and a solution of an inorganic acid such as hydrochloric acid, sulfuric acid, phosphoric acid, etc.
Accordingly, oxidation doping can be also carried out by a process of first forming an imino-p-phenylene type polyaniline film by casting an imino-p-phenylene type polyaniline solution and then immersing the film in an aqueous solution of an oxidizing agent such as ferric chloride, etc., in place of the above-described process of forming the film after adding the oxidizing agent to the polyaniline solution. The oxidation doping is different from protonic acid doping in the point that an oxidation reaction is accompanied
In general, oxidation doping has an advantage that the required time may be short as compared with protonic acid doping but on the other hand, since, for example, when an oxidizing agent such as ferric chloride is used, hydrogen chloride is a dopant and when a combination of hydrogen peroxide and methanesulfonic acid is used, methanesulfonic acid is a dopant, there is a problem in the stability of the electrical conductivity after doping the polyaniline film. Further, when hydrogen peroxide is used as an oxidizing agent, there is the problem in that the mechanical strength of the polyaniline film is decreased by the doping treatment.